/*
 * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
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 *
 *
 *
 *
 */

package java.util;

import java.lang.ref.WeakReference;
import java.lang.ref.ReferenceQueue;
import java.util.concurrent.ThreadLocalRandom;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Consumer;


/**
 * Hash table based implementation of the <tt>Map</tt> interface, with
 * <em>weak keys</em>.
 * An entry in a <tt>WeakHashMap</tt> will automatically be removed when
 * its key is no longer in ordinary use.  More precisely, the presence of a
 * mapping for a given key will not prevent the key from being discarded by the
 * garbage collector, that is, made finalizable, finalized, and then reclaimed.
 * When a key has been discarded its entry is effectively removed from the map,
 * so this class behaves somewhat differently from other <tt>Map</tt>
 * implementations.
 *
 * <p> Both null values and the null key are supported. This class has
 * performance characteristics similar to those of the <tt>HashMap</tt>
 * class, and has the same efficiency parameters of <em>initial capacity</em>
 * and <em>load factor</em>.
 *
 * <p> Like most collection classes, this class is not synchronized.
 * A synchronized <tt>WeakHashMap</tt> may be constructed using the
 * {@link Collections#synchronizedMap Collections.synchronizedMap}
 * method.
 *
 * <p> This class is intended primarily for use with key objects whose
 * <tt>equals</tt> methods test for object identity using the
 * <tt>==</tt> operator.  Once such a key is discarded it can never be
 * recreated, so it is impossible to do a lookup of that key in a
 * <tt>WeakHashMap</tt> at some later time and be surprised that its entry
 * has been removed.  This class will work perfectly well with key objects
 * whose <tt>equals</tt> methods are not based upon object identity, such
 * as <tt>String</tt> instances.  With such recreatable key objects,
 * however, the automatic removal of <tt>WeakHashMap</tt> entries whose
 * keys have been discarded may prove to be confusing.
 *
 * <p> The behavior of the <tt>WeakHashMap</tt> class depends in part upon
 * the actions of the garbage collector, so several familiar (though not
 * required) <tt>Map</tt> invariants do not hold for this class.  Because
 * the garbage collector may discard keys at any time, a
 * <tt>WeakHashMap</tt> may behave as though an unknown thread is silently
 * removing entries.  In particular, even if you synchronize on a
 * <tt>WeakHashMap</tt> instance and invoke none of its mutator methods, it
 * is possible for the <tt>size</tt> method to return smaller values over
 * time, for the <tt>isEmpty</tt> method to return <tt>false</tt> and
 * then <tt>true</tt>, for the <tt>containsKey</tt> method to return
 * <tt>true</tt> and later <tt>false</tt> for a given key, for the
 * <tt>get</tt> method to return a value for a given key but later return
 * <tt>null</tt>, for the <tt>put</tt> method to return
 * <tt>null</tt> and the <tt>remove</tt> method to return
 * <tt>false</tt> for a key that previously appeared to be in the map, and
 * for successive examinations of the key set, the value collection, and
 * the entry set to yield successively smaller numbers of elements.
 *
 * <p> Each key object in a <tt>WeakHashMap</tt> is stored indirectly as
 * the referent of a weak reference.  Therefore a key will automatically be
 * removed only after the weak references to it, both inside and outside of the
 * map, have been cleared by the garbage collector.
 *
 * <p> <strong>Implementation note:</strong> The value objects in a
 * <tt>WeakHashMap</tt> are held by ordinary strong references.  Thus care
 * should be taken to ensure that value objects do not strongly refer to their
 * own keys, either directly or indirectly, since that will prevent the keys
 * from being discarded.  Note that a value object may refer indirectly to its
 * key via the <tt>WeakHashMap</tt> itself; that is, a value object may
 * strongly refer to some other key object whose associated value object, in
 * turn, strongly refers to the key of the first value object.  If the values
 * in the map do not rely on the map holding strong references to them, one way
 * to deal with this is to wrap values themselves within
 * <tt>WeakReferences</tt> before
 * inserting, as in: <tt>m.put(key, new WeakReference(value))</tt>,
 * and then unwrapping upon each <tt>get</tt>.
 *
 * <p>The iterators returned by the <tt>iterator</tt> method of the collections
 * returned by all of this class's "collection view methods" are
 * <i>fail-fast</i>: if the map is structurally modified at any time after the
 * iterator is created, in any way except through the iterator's own
 * <tt>remove</tt> method, the iterator will throw a {@link
 * ConcurrentModificationException}.  Thus, in the face of concurrent
 * modification, the iterator fails quickly and cleanly, rather than risking
 * arbitrary, non-deterministic behavior at an undetermined time in the future.
 *
 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
 * as it is, generally speaking, impossible to make any hard guarantees in the
 * presence of unsynchronized concurrent modification.  Fail-fast iterators
 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
 * Therefore, it would be wrong to write a program that depended on this
 * exception for its correctness:  <i>the fail-fast behavior of iterators
 * should be used only to detect bugs.</i>
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param <K> the type of keys maintained by this map
 * @param <V> the type of mapped values
 * @author Doug Lea
 * @author Josh Bloch
 * @author Mark Reinhold
 * @see java.util.HashMap
 * @see java.lang.ref.WeakReference
 * @since 1.2
 */
public class WeakHashMap<K, V>
    extends AbstractMap<K, V>
    implements Map<K, V> {

  /**
   * The default initial capacity -- MUST be a power of two.
   */
  private static final int DEFAULT_INITIAL_CAPACITY = 16;

  /**
   * The maximum capacity, used if a higher value is implicitly specified
   * by either of the constructors with arguments.
   * MUST be a power of two <= 1<<30.
   */
  private static final int MAXIMUM_CAPACITY = 1 << 30;

  /**
   * The load factor used when none specified in constructor.
   */
  private static final float DEFAULT_LOAD_FACTOR = 0.75f;

  /**
   * The table, resized as necessary. Length MUST Always be a power of two.
   */
  Entry<K, V>[] table;

  /**
   * The number of key-value mappings contained in this weak hash map.
   */
  private int size;

  /**
   * The next size value at which to resize (capacity * load factor).
   */
  private int threshold;

  /**
   * The load factor for the hash table.
   */
  private final float loadFactor;

  /**
   * Reference queue for cleared WeakEntries
   */
  private final ReferenceQueue<Object> queue = new ReferenceQueue<>();

  /**
   * The number of times this WeakHashMap has been structurally modified.
   * Structural modifications are those that change the number of
   * mappings in the map or otherwise modify its internal structure
   * (e.g., rehash).  This field is used to make iterators on
   * Collection-views of the map fail-fast.
   *
   * @see ConcurrentModificationException
   */
  int modCount;

  @SuppressWarnings("unchecked")
  private Entry<K, V>[] newTable(int n) {
    return (Entry<K, V>[]) new Entry<?, ?>[n];
  }

  /**
   * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial
   * capacity and the given load factor.
   *
   * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt>
   * @param loadFactor The load factor of the <tt>WeakHashMap</tt>
   * @throws IllegalArgumentException if the initial capacity is negative, or if the load factor is
   * nonpositive.
   */
  public WeakHashMap(int initialCapacity, float loadFactor) {
    if (initialCapacity < 0) {
      throw new IllegalArgumentException("Illegal Initial Capacity: " +
          initialCapacity);
    }
    if (initialCapacity > MAXIMUM_CAPACITY) {
      initialCapacity = MAXIMUM_CAPACITY;
    }

    if (loadFactor <= 0 || Float.isNaN(loadFactor)) {
      throw new IllegalArgumentException("Illegal Load factor: " +
          loadFactor);
    }
    int capacity = 1;
    while (capacity < initialCapacity) {
      capacity <<= 1;
    }
    table = newTable(capacity);
    this.loadFactor = loadFactor;
    threshold = (int) (capacity * loadFactor);
  }

  /**
   * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial
   * capacity and the default load factor (0.75).
   *
   * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt>
   * @throws IllegalArgumentException if the initial capacity is negative
   */
  public WeakHashMap(int initialCapacity) {
    this(initialCapacity, DEFAULT_LOAD_FACTOR);
  }

  /**
   * Constructs a new, empty <tt>WeakHashMap</tt> with the default initial
   * capacity (16) and load factor (0.75).
   */
  public WeakHashMap() {
    this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
  }

  /**
   * Constructs a new <tt>WeakHashMap</tt> with the same mappings as the
   * specified map.  The <tt>WeakHashMap</tt> is created with the default
   * load factor (0.75) and an initial capacity sufficient to hold the
   * mappings in the specified map.
   *
   * @param m the map whose mappings are to be placed in this map
   * @throws NullPointerException if the specified map is null
   * @since 1.3
   */
  public WeakHashMap(Map<? extends K, ? extends V> m) {
    this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
        DEFAULT_INITIAL_CAPACITY),
        DEFAULT_LOAD_FACTOR);
    putAll(m);
  }

  // internal utilities

  /**
   * Value representing null keys inside tables.
   */
  private static final Object NULL_KEY = new Object();

  /**
   * Use NULL_KEY for key if it is null.
   */
  private static Object maskNull(Object key) {
    return (key == null) ? NULL_KEY : key;
  }

  /**
   * Returns internal representation of null key back to caller as null.
   */
  static Object unmaskNull(Object key) {
    return (key == NULL_KEY) ? null : key;
  }

  /**
   * Checks for equality of non-null reference x and possibly-null y.  By
   * default uses Object.equals.
   */
  private static boolean eq(Object x, Object y) {
    return x == y || x.equals(y);
  }

  /**
   * Retrieve object hash code and applies a supplemental hash function to the
   * result hash, which defends against poor quality hash functions.  This is
   * critical because HashMap uses power-of-two length hash tables, that
   * otherwise encounter collisions for hashCodes that do not differ
   * in lower bits.
   */
  final int hash(Object k) {
    int h = k.hashCode();

    // This function ensures that hashCodes that differ only by
    // constant multiples at each bit position have a bounded
    // number of collisions (approximately 8 at default load factor).
    h ^= (h >>> 20) ^ (h >>> 12);
    return h ^ (h >>> 7) ^ (h >>> 4);
  }

  /**
   * Returns index for hash code h.
   */
  private static int indexFor(int h, int length) {
    return h & (length - 1);
  }

  /**
   * Expunges stale entries from the table.
   */
  private void expungeStaleEntries() {
    for (Object x; (x = queue.poll()) != null; ) {
      synchronized (queue) {
        @SuppressWarnings("unchecked")
        Entry<K, V> e = (Entry<K, V>) x;
        int i = indexFor(e.hash, table.length);

        Entry<K, V> prev = table[i];
        Entry<K, V> p = prev;
        while (p != null) {
          Entry<K, V> next = p.next;
          if (p == e) {
            if (prev == e) {
              table[i] = next;
            } else {
              prev.next = next;
            }
            // Must not null out e.next;
            // stale entries may be in use by a HashIterator
            e.value = null; // Help GC
            size--;
            break;
          }
          prev = p;
          p = next;
        }
      }
    }
  }

  /**
   * Returns the table after first expunging stale entries.
   */
  private Entry<K, V>[] getTable() {
    expungeStaleEntries();
    return table;
  }

  /**
   * Returns the number of key-value mappings in this map.
   * This result is a snapshot, and may not reflect unprocessed
   * entries that will be removed before next attempted access
   * because they are no longer referenced.
   */
  public int size() {
    if (size == 0) {
      return 0;
    }
    expungeStaleEntries();
    return size;
  }

  /**
   * Returns <tt>true</tt> if this map contains no key-value mappings.
   * This result is a snapshot, and may not reflect unprocessed
   * entries that will be removed before next attempted access
   * because they are no longer referenced.
   */
  public boolean isEmpty() {
    return size() == 0;
  }

  /**
   * Returns the value to which the specified key is mapped,
   * or {@code null} if this map contains no mapping for the key.
   *
   * <p>More formally, if this map contains a mapping from a key
   * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
   * key.equals(k))}, then this method returns {@code v}; otherwise
   * it returns {@code null}.  (There can be at most one such mapping.)
   *
   * <p>A return value of {@code null} does not <i>necessarily</i>
   * indicate that the map contains no mapping for the key; it's also
   * possible that the map explicitly maps the key to {@code null}.
   * The {@link #containsKey containsKey} operation may be used to
   * distinguish these two cases.
   *
   * @see #put(Object, Object)
   */
  public V get(Object key) {
    Object k = maskNull(key);
    int h = hash(k);
    Entry<K, V>[] tab = getTable();
    int index = indexFor(h, tab.length);
    Entry<K, V> e = tab[index];
    while (e != null) {
      if (e.hash == h && eq(k, e.get())) {
        return e.value;
      }
      e = e.next;
    }
    return null;
  }

  /**
   * Returns <tt>true</tt> if this map contains a mapping for the
   * specified key.
   *
   * @param key The key whose presence in this map is to be tested
   * @return <tt>true</tt> if there is a mapping for <tt>key</tt>; <tt>false</tt> otherwise
   */
  public boolean containsKey(Object key) {
    return getEntry(key) != null;
  }

  /**
   * Returns the entry associated with the specified key in this map.
   * Returns null if the map contains no mapping for this key.
   */
  Entry<K, V> getEntry(Object key) {
    Object k = maskNull(key);
    int h = hash(k);
    Entry<K, V>[] tab = getTable();
    int index = indexFor(h, tab.length);
    Entry<K, V> e = tab[index];
    while (e != null && !(e.hash == h && eq(k, e.get()))) {
      e = e.next;
    }
    return e;
  }

  /**
   * Associates the specified value with the specified key in this map.
   * If the map previously contained a mapping for this key, the old
   * value is replaced.
   *
   * @param key key with which the specified value is to be associated.
   * @param value value to be associated with the specified key.
   * @return the previous value associated with <tt>key</tt>, or <tt>null</tt> if there was no
   * mapping for <tt>key</tt>. (A <tt>null</tt> return can also indicate that the map previously
   * associated <tt>null</tt> with <tt>key</tt>.)
   */
  public V put(K key, V value) {
    Object k = maskNull(key);
    int h = hash(k);
    Entry<K, V>[] tab = getTable();
    int i = indexFor(h, tab.length);

    for (Entry<K, V> e = tab[i]; e != null; e = e.next) {
      if (h == e.hash && eq(k, e.get())) {
        V oldValue = e.value;
        if (value != oldValue) {
          e.value = value;
        }
        return oldValue;
      }
    }

    modCount++;
    Entry<K, V> e = tab[i];
    tab[i] = new Entry<>(k, value, queue, h, e);
    if (++size >= threshold) {
      resize(tab.length * 2);
    }
    return null;
  }

  /**
   * Rehashes the contents of this map into a new array with a
   * larger capacity.  This method is called automatically when the
   * number of keys in this map reaches its threshold.
   *
   * If current capacity is MAXIMUM_CAPACITY, this method does not
   * resize the map, but sets threshold to Integer.MAX_VALUE.
   * This has the effect of preventing future calls.
   *
   * @param newCapacity the new capacity, MUST be a power of two; must be greater than current
   * capacity unless current capacity is MAXIMUM_CAPACITY (in which case value is irrelevant).
   */
  void resize(int newCapacity) {
    Entry<K, V>[] oldTable = getTable();
    int oldCapacity = oldTable.length;
    if (oldCapacity == MAXIMUM_CAPACITY) {
      threshold = Integer.MAX_VALUE;
      return;
    }

    Entry<K, V>[] newTable = newTable(newCapacity);
    transfer(oldTable, newTable);
    table = newTable;

        /*
         * If ignoring null elements and processing ref queue caused massive
         * shrinkage, then restore old table.  This should be rare, but avoids
         * unbounded expansion of garbage-filled tables.
         */
    if (size >= threshold / 2) {
      threshold = (int) (newCapacity * loadFactor);
    } else {
      expungeStaleEntries();
      transfer(newTable, oldTable);
      table = oldTable;
    }
  }

  /**
   * Transfers all entries from src to dest tables
   */
  private void transfer(Entry<K, V>[] src, Entry<K, V>[] dest) {
    for (int j = 0; j < src.length; ++j) {
      Entry<K, V> e = src[j];
      src[j] = null;
      while (e != null) {
        Entry<K, V> next = e.next;
        Object key = e.get();
        if (key == null) {
          e.next = null;  // Help GC
          e.value = null; //  "   "
          size--;
        } else {
          int i = indexFor(e.hash, dest.length);
          e.next = dest[i];
          dest[i] = e;
        }
        e = next;
      }
    }
  }

  /**
   * Copies all of the mappings from the specified map to this map.
   * These mappings will replace any mappings that this map had for any
   * of the keys currently in the specified map.
   *
   * @param m mappings to be stored in this map.
   * @throws NullPointerException if the specified map is null.
   */
  public void putAll(Map<? extends K, ? extends V> m) {
    int numKeysToBeAdded = m.size();
    if (numKeysToBeAdded == 0) {
      return;
    }

        /*
         * Expand the map if the map if the number of mappings to be added
         * is greater than or equal to threshold.  This is conservative; the
         * obvious condition is (m.size() + size) >= threshold, but this
         * condition could result in a map with twice the appropriate capacity,
         * if the keys to be added overlap with the keys already in this map.
         * By using the conservative calculation, we subject ourself
         * to at most one extra resize.
         */
    if (numKeysToBeAdded > threshold) {
      int targetCapacity = (int) (numKeysToBeAdded / loadFactor + 1);
      if (targetCapacity > MAXIMUM_CAPACITY) {
        targetCapacity = MAXIMUM_CAPACITY;
      }
      int newCapacity = table.length;
      while (newCapacity < targetCapacity) {
        newCapacity <<= 1;
      }
      if (newCapacity > table.length) {
        resize(newCapacity);
      }
    }

    for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) {
      put(e.getKey(), e.getValue());
    }
  }

  /**
   * Removes the mapping for a key from this weak hash map if it is present.
   * More formally, if this map contains a mapping from key <tt>k</tt> to
   * value <tt>v</tt> such that <code>(key==null ?  k==null :
   * key.equals(k))</code>, that mapping is removed.  (The map can contain
   * at most one such mapping.)
   *
   * <p>Returns the value to which this map previously associated the key,
   * or <tt>null</tt> if the map contained no mapping for the key.  A
   * return value of <tt>null</tt> does not <i>necessarily</i> indicate
   * that the map contained no mapping for the key; it's also possible
   * that the map explicitly mapped the key to <tt>null</tt>.
   *
   * <p>The map will not contain a mapping for the specified key once the
   * call returns.
   *
   * @param key key whose mapping is to be removed from the map
   * @return the previous value associated with <tt>key</tt>, or <tt>null</tt> if there was no
   * mapping for <tt>key</tt>
   */
  public V remove(Object key) {
    Object k = maskNull(key);
    int h = hash(k);
    Entry<K, V>[] tab = getTable();
    int i = indexFor(h, tab.length);
    Entry<K, V> prev = tab[i];
    Entry<K, V> e = prev;

    while (e != null) {
      Entry<K, V> next = e.next;
      if (h == e.hash && eq(k, e.get())) {
        modCount++;
        size--;
        if (prev == e) {
          tab[i] = next;
        } else {
          prev.next = next;
        }
        return e.value;
      }
      prev = e;
      e = next;
    }

    return null;
  }

  /**
   * Special version of remove needed by Entry set
   */
  boolean removeMapping(Object o) {
    if (!(o instanceof Map.Entry)) {
      return false;
    }
    Entry<K, V>[] tab = getTable();
    Map.Entry<?, ?> entry = (Map.Entry<?, ?>) o;
    Object k = maskNull(entry.getKey());
    int h = hash(k);
    int i = indexFor(h, tab.length);
    Entry<K, V> prev = tab[i];
    Entry<K, V> e = prev;

    while (e != null) {
      Entry<K, V> next = e.next;
      if (h == e.hash && e.equals(entry)) {
        modCount++;
        size--;
        if (prev == e) {
          tab[i] = next;
        } else {
          prev.next = next;
        }
        return true;
      }
      prev = e;
      e = next;
    }

    return false;
  }

  /**
   * Removes all of the mappings from this map.
   * The map will be empty after this call returns.
   */
  public void clear() {
    // clear out ref queue. We don't need to expunge entries
    // since table is getting cleared.
    while (queue.poll() != null) {
      ;
    }

    modCount++;
    Arrays.fill(table, null);
    size = 0;

    // Allocation of array may have caused GC, which may have caused
    // additional entries to go stale.  Removing these entries from the
    // reference queue will make them eligible for reclamation.
    while (queue.poll() != null) {
      ;
    }
  }

  /**
   * Returns <tt>true</tt> if this map maps one or more keys to the
   * specified value.
   *
   * @param value value whose presence in this map is to be tested
   * @return <tt>true</tt> if this map maps one or more keys to the specified value
   */
  public boolean containsValue(Object value) {
    if (value == null) {
      return containsNullValue();
    }

    Entry<K, V>[] tab = getTable();
    for (int i = tab.length; i-- > 0; ) {
      for (Entry<K, V> e = tab[i]; e != null; e = e.next) {
        if (value.equals(e.value)) {
          return true;
        }
      }
    }
    return false;
  }

  /**
   * Special-case code for containsValue with null argument
   */
  private boolean containsNullValue() {
    Entry<K, V>[] tab = getTable();
    for (int i = tab.length; i-- > 0; ) {
      for (Entry<K, V> e = tab[i]; e != null; e = e.next) {
        if (e.value == null) {
          return true;
        }
      }
    }
    return false;
  }

  /**
   * The entries in this hash table extend WeakReference, using its main ref
   * field as the key.
   */
  private static class Entry<K, V> extends WeakReference<Object> implements Map.Entry<K, V> {

    V value;
    final int hash;
    Entry<K, V> next;

    /**
     * Creates new entry.
     */
    Entry(Object key, V value,
        ReferenceQueue<Object> queue,
        int hash, Entry<K, V> next) {
      super(key, queue);
      this.value = value;
      this.hash = hash;
      this.next = next;
    }

    @SuppressWarnings("unchecked")
    public K getKey() {
      return (K) WeakHashMap.unmaskNull(get());
    }

    public V getValue() {
      return value;
    }

    public V setValue(V newValue) {
      V oldValue = value;
      value = newValue;
      return oldValue;
    }

    public boolean equals(Object o) {
      if (!(o instanceof Map.Entry)) {
        return false;
      }
      Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
      K k1 = getKey();
      Object k2 = e.getKey();
      if (k1 == k2 || (k1 != null && k1.equals(k2))) {
        V v1 = getValue();
        Object v2 = e.getValue();
        if (v1 == v2 || (v1 != null && v1.equals(v2))) {
          return true;
        }
      }
      return false;
    }

    public int hashCode() {
      K k = getKey();
      V v = getValue();
      return Objects.hashCode(k) ^ Objects.hashCode(v);
    }

    public String toString() {
      return getKey() + "=" + getValue();
    }
  }

  private abstract class HashIterator<T> implements Iterator<T> {

    private int index;
    private Entry<K, V> entry;
    private Entry<K, V> lastReturned;
    private int expectedModCount = modCount;

    /**
     * Strong reference needed to avoid disappearance of key
     * between hasNext and next
     */
    private Object nextKey;

    /**
     * Strong reference needed to avoid disappearance of key
     * between nextEntry() and any use of the entry
     */
    private Object currentKey;

    HashIterator() {
      index = isEmpty() ? 0 : table.length;
    }

    public boolean hasNext() {
      Entry<K, V>[] t = table;

      while (nextKey == null) {
        Entry<K, V> e = entry;
        int i = index;
        while (e == null && i > 0) {
          e = t[--i];
        }
        entry = e;
        index = i;
        if (e == null) {
          currentKey = null;
          return false;
        }
        nextKey = e.get(); // hold on to key in strong ref
        if (nextKey == null) {
          entry = entry.next;
        }
      }
      return true;
    }

    /**
     * The common parts of next() across different types of iterators
     */
    protected Entry<K, V> nextEntry() {
      if (modCount != expectedModCount) {
        throw new ConcurrentModificationException();
      }
      if (nextKey == null && !hasNext()) {
        throw new NoSuchElementException();
      }

      lastReturned = entry;
      entry = entry.next;
      currentKey = nextKey;
      nextKey = null;
      return lastReturned;
    }

    public void remove() {
      if (lastReturned == null) {
        throw new IllegalStateException();
      }
      if (modCount != expectedModCount) {
        throw new ConcurrentModificationException();
      }

      WeakHashMap.this.remove(currentKey);
      expectedModCount = modCount;
      lastReturned = null;
      currentKey = null;
    }

  }

  private class ValueIterator extends HashIterator<V> {

    public V next() {
      return nextEntry().value;
    }
  }

  private class KeyIterator extends HashIterator<K> {

    public K next() {
      return nextEntry().getKey();
    }
  }

  private class EntryIterator extends HashIterator<Map.Entry<K, V>> {

    public Map.Entry<K, V> next() {
      return nextEntry();
    }
  }

  // Views

  private transient Set<Map.Entry<K, V>> entrySet;

  /**
   * Returns a {@link Set} view of the keys contained in this map.
   * The set is backed by the map, so changes to the map are
   * reflected in the set, and vice-versa.  If the map is modified
   * while an iteration over the set is in progress (except through
   * the iterator's own <tt>remove</tt> operation), the results of
   * the iteration are undefined.  The set supports element removal,
   * which removes the corresponding mapping from the map, via the
   * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
   * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
   * operations.  It does not support the <tt>add</tt> or <tt>addAll</tt>
   * operations.
   */
  public Set<K> keySet() {
    Set<K> ks = keySet;
    return (ks != null ? ks : (keySet = new KeySet()));
  }

  private class KeySet extends AbstractSet<K> {

    public Iterator<K> iterator() {
      return new KeyIterator();
    }

    public int size() {
      return WeakHashMap.this.size();
    }

    public boolean contains(Object o) {
      return containsKey(o);
    }

    public boolean remove(Object o) {
      if (containsKey(o)) {
        WeakHashMap.this.remove(o);
        return true;
      } else {
        return false;
      }
    }

    public void clear() {
      WeakHashMap.this.clear();
    }

    public Spliterator<K> spliterator() {
      return new KeySpliterator<>(WeakHashMap.this, 0, -1, 0, 0);
    }
  }

  /**
   * Returns a {@link Collection} view of the values contained in this map.
   * The collection is backed by the map, so changes to the map are
   * reflected in the collection, and vice-versa.  If the map is
   * modified while an iteration over the collection is in progress
   * (except through the iterator's own <tt>remove</tt> operation),
   * the results of the iteration are undefined.  The collection
   * supports element removal, which removes the corresponding
   * mapping from the map, via the <tt>Iterator.remove</tt>,
   * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
   * <tt>retainAll</tt> and <tt>clear</tt> operations.  It does not
   * support the <tt>add</tt> or <tt>addAll</tt> operations.
   */
  public Collection<V> values() {
    Collection<V> vs = values;
    return (vs != null) ? vs : (values = new Values());
  }

  private class Values extends AbstractCollection<V> {

    public Iterator<V> iterator() {
      return new ValueIterator();
    }

    public int size() {
      return WeakHashMap.this.size();
    }

    public boolean contains(Object o) {
      return containsValue(o);
    }

    public void clear() {
      WeakHashMap.this.clear();
    }

    public Spliterator<V> spliterator() {
      return new ValueSpliterator<>(WeakHashMap.this, 0, -1, 0, 0);
    }
  }

  /**
   * Returns a {@link Set} view of the mappings contained in this map.
   * The set is backed by the map, so changes to the map are
   * reflected in the set, and vice-versa.  If the map is modified
   * while an iteration over the set is in progress (except through
   * the iterator's own <tt>remove</tt> operation, or through the
   * <tt>setValue</tt> operation on a map entry returned by the
   * iterator) the results of the iteration are undefined.  The set
   * supports element removal, which removes the corresponding
   * mapping from the map, via the <tt>Iterator.remove</tt>,
   * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
   * <tt>clear</tt> operations.  It does not support the
   * <tt>add</tt> or <tt>addAll</tt> operations.
   */
  public Set<Map.Entry<K, V>> entrySet() {
    Set<Map.Entry<K, V>> es = entrySet;
    return es != null ? es : (entrySet = new EntrySet());
  }

  private class EntrySet extends AbstractSet<Map.Entry<K, V>> {

    public Iterator<Map.Entry<K, V>> iterator() {
      return new EntryIterator();
    }

    public boolean contains(Object o) {
      if (!(o instanceof Map.Entry)) {
        return false;
      }
      Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
      Entry<K, V> candidate = getEntry(e.getKey());
      return candidate != null && candidate.equals(e);
    }

    public boolean remove(Object o) {
      return removeMapping(o);
    }

    public int size() {
      return WeakHashMap.this.size();
    }

    public void clear() {
      WeakHashMap.this.clear();
    }

    private List<Map.Entry<K, V>> deepCopy() {
      List<Map.Entry<K, V>> list = new ArrayList<>(size());
      for (Map.Entry<K, V> e : this) {
        list.add(new AbstractMap.SimpleEntry<>(e));
      }
      return list;
    }

    public Object[] toArray() {
      return deepCopy().toArray();
    }

    public <T> T[] toArray(T[] a) {
      return deepCopy().toArray(a);
    }

    public Spliterator<Map.Entry<K, V>> spliterator() {
      return new EntrySpliterator<>(WeakHashMap.this, 0, -1, 0, 0);
    }
  }

  @SuppressWarnings("unchecked")
  @Override
  public void forEach(BiConsumer<? super K, ? super V> action) {
    Objects.requireNonNull(action);
    int expectedModCount = modCount;

    Entry<K, V>[] tab = getTable();
    for (Entry<K, V> entry : tab) {
      while (entry != null) {
        Object key = entry.get();
        if (key != null) {
          action.accept((K) WeakHashMap.unmaskNull(key), entry.value);
        }
        entry = entry.next;

        if (expectedModCount != modCount) {
          throw new ConcurrentModificationException();
        }
      }
    }
  }

  @SuppressWarnings("unchecked")
  @Override
  public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
    Objects.requireNonNull(function);
    int expectedModCount = modCount;

    Entry<K, V>[] tab = getTable();
    ;
    for (Entry<K, V> entry : tab) {
      while (entry != null) {
        Object key = entry.get();
        if (key != null) {
          entry.value = function.apply((K) WeakHashMap.unmaskNull(key), entry.value);
        }
        entry = entry.next;

        if (expectedModCount != modCount) {
          throw new ConcurrentModificationException();
        }
      }
    }
  }

  /**
   * Similar form as other hash Spliterators, but skips dead
   * elements.
   */
  static class WeakHashMapSpliterator<K, V> {

    final WeakHashMap<K, V> map;
    WeakHashMap.Entry<K, V> current; // current node
    int index;             // current index, modified on advance/split
    int fence;             // -1 until first use; then one past last index
    int est;               // size estimate
    int expectedModCount;  // for comodification checks

    WeakHashMapSpliterator(WeakHashMap<K, V> m, int origin,
        int fence, int est,
        int expectedModCount) {
      this.map = m;
      this.index = origin;
      this.fence = fence;
      this.est = est;
      this.expectedModCount = expectedModCount;
    }

    final int getFence() { // initialize fence and size on first use
      int hi;
      if ((hi = fence) < 0) {
        WeakHashMap<K, V> m = map;
        est = m.size();
        expectedModCount = m.modCount;
        hi = fence = m.table.length;
      }
      return hi;
    }

    public final long estimateSize() {
      getFence(); // force init
      return (long) est;
    }
  }

  static final class KeySpliterator<K, V>
      extends WeakHashMapSpliterator<K, V>
      implements Spliterator<K> {

    KeySpliterator(WeakHashMap<K, V> m, int origin, int fence, int est,
        int expectedModCount) {
      super(m, origin, fence, est, expectedModCount);
    }

    public KeySpliterator<K, V> trySplit() {
      int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
      return (lo >= mid) ? null :
          new KeySpliterator<K, V>(map, lo, index = mid, est >>>= 1,
              expectedModCount);
    }

    public void forEachRemaining(Consumer<? super K> action) {
      int i, hi, mc;
      if (action == null) {
        throw new NullPointerException();
      }
      WeakHashMap<K, V> m = map;
      WeakHashMap.Entry<K, V>[] tab = m.table;
      if ((hi = fence) < 0) {
        mc = expectedModCount = m.modCount;
        hi = fence = tab.length;
      } else {
        mc = expectedModCount;
      }
      if (tab.length >= hi && (i = index) >= 0 &&
          (i < (index = hi) || current != null)) {
        WeakHashMap.Entry<K, V> p = current;
        current = null; // exhaust
        do {
          if (p == null) {
            p = tab[i++];
          } else {
            Object x = p.get();
            p = p.next;
            if (x != null) {
              @SuppressWarnings("unchecked") K k =
                  (K) WeakHashMap.unmaskNull(x);
              action.accept(k);
            }
          }
        } while (p != null || i < hi);
      }
      if (m.modCount != mc) {
        throw new ConcurrentModificationException();
      }
    }

    public boolean tryAdvance(Consumer<? super K> action) {
      int hi;
      if (action == null) {
        throw new NullPointerException();
      }
      WeakHashMap.Entry<K, V>[] tab = map.table;
      if (tab.length >= (hi = getFence()) && index >= 0) {
        while (current != null || index < hi) {
          if (current == null) {
            current = tab[index++];
          } else {
            Object x = current.get();
            current = current.next;
            if (x != null) {
              @SuppressWarnings("unchecked") K k =
                  (K) WeakHashMap.unmaskNull(x);
              action.accept(k);
              if (map.modCount != expectedModCount) {
                throw new ConcurrentModificationException();
              }
              return true;
            }
          }
        }
      }
      return false;
    }

    public int characteristics() {
      return Spliterator.DISTINCT;
    }
  }

  static final class ValueSpliterator<K, V>
      extends WeakHashMapSpliterator<K, V>
      implements Spliterator<V> {

    ValueSpliterator(WeakHashMap<K, V> m, int origin, int fence, int est,
        int expectedModCount) {
      super(m, origin, fence, est, expectedModCount);
    }

    public ValueSpliterator<K, V> trySplit() {
      int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
      return (lo >= mid) ? null :
          new ValueSpliterator<K, V>(map, lo, index = mid, est >>>= 1,
              expectedModCount);
    }

    public void forEachRemaining(Consumer<? super V> action) {
      int i, hi, mc;
      if (action == null) {
        throw new NullPointerException();
      }
      WeakHashMap<K, V> m = map;
      WeakHashMap.Entry<K, V>[] tab = m.table;
      if ((hi = fence) < 0) {
        mc = expectedModCount = m.modCount;
        hi = fence = tab.length;
      } else {
        mc = expectedModCount;
      }
      if (tab.length >= hi && (i = index) >= 0 &&
          (i < (index = hi) || current != null)) {
        WeakHashMap.Entry<K, V> p = current;
        current = null; // exhaust
        do {
          if (p == null) {
            p = tab[i++];
          } else {
            Object x = p.get();
            V v = p.value;
            p = p.next;
            if (x != null) {
              action.accept(v);
            }
          }
        } while (p != null || i < hi);
      }
      if (m.modCount != mc) {
        throw new ConcurrentModificationException();
      }
    }

    public boolean tryAdvance(Consumer<? super V> action) {
      int hi;
      if (action == null) {
        throw new NullPointerException();
      }
      WeakHashMap.Entry<K, V>[] tab = map.table;
      if (tab.length >= (hi = getFence()) && index >= 0) {
        while (current != null || index < hi) {
          if (current == null) {
            current = tab[index++];
          } else {
            Object x = current.get();
            V v = current.value;
            current = current.next;
            if (x != null) {
              action.accept(v);
              if (map.modCount != expectedModCount) {
                throw new ConcurrentModificationException();
              }
              return true;
            }
          }
        }
      }
      return false;
    }

    public int characteristics() {
      return 0;
    }
  }

  static final class EntrySpliterator<K, V>
      extends WeakHashMapSpliterator<K, V>
      implements Spliterator<Map.Entry<K, V>> {

    EntrySpliterator(WeakHashMap<K, V> m, int origin, int fence, int est,
        int expectedModCount) {
      super(m, origin, fence, est, expectedModCount);
    }

    public EntrySpliterator<K, V> trySplit() {
      int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
      return (lo >= mid) ? null :
          new EntrySpliterator<K, V>(map, lo, index = mid, est >>>= 1,
              expectedModCount);
    }


    public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) {
      int i, hi, mc;
      if (action == null) {
        throw new NullPointerException();
      }
      WeakHashMap<K, V> m = map;
      WeakHashMap.Entry<K, V>[] tab = m.table;
      if ((hi = fence) < 0) {
        mc = expectedModCount = m.modCount;
        hi = fence = tab.length;
      } else {
        mc = expectedModCount;
      }
      if (tab.length >= hi && (i = index) >= 0 &&
          (i < (index = hi) || current != null)) {
        WeakHashMap.Entry<K, V> p = current;
        current = null; // exhaust
        do {
          if (p == null) {
            p = tab[i++];
          } else {
            Object x = p.get();
            V v = p.value;
            p = p.next;
            if (x != null) {
              @SuppressWarnings("unchecked") K k =
                  (K) WeakHashMap.unmaskNull(x);
              action.accept
                  (new AbstractMap.SimpleImmutableEntry<K, V>(k, v));
            }
          }
        } while (p != null || i < hi);
      }
      if (m.modCount != mc) {
        throw new ConcurrentModificationException();
      }
    }

    public boolean tryAdvance(Consumer<? super Map.Entry<K, V>> action) {
      int hi;
      if (action == null) {
        throw new NullPointerException();
      }
      WeakHashMap.Entry<K, V>[] tab = map.table;
      if (tab.length >= (hi = getFence()) && index >= 0) {
        while (current != null || index < hi) {
          if (current == null) {
            current = tab[index++];
          } else {
            Object x = current.get();
            V v = current.value;
            current = current.next;
            if (x != null) {
              @SuppressWarnings("unchecked") K k =
                  (K) WeakHashMap.unmaskNull(x);
              action.accept
                  (new AbstractMap.SimpleImmutableEntry<K, V>(k, v));
              if (map.modCount != expectedModCount) {
                throw new ConcurrentModificationException();
              }
              return true;
            }
          }
        }
      }
      return false;
    }

    public int characteristics() {
      return Spliterator.DISTINCT;
    }
  }

}
